HOOD-6816 Keep linked comment windows open after rendering

engine/app/javascript/controllers/coplan/text_selection_controller.js

@@ -551,7 +551,10 @@ export default class extends Controller {
     // Margin cards survive re-highlighting; keep the window beside its card.
     if (this._activeMark?.isConnected && this._activeMark.closest(".comment-margin")) return
 
-    const replacementMark = this.contentTarget.querySelector(`.anchor-highlight[data-thread-id="${threadId}"]`)
+    // Document and earlier-text discussions have list entries instead of
+    // inline marks. Rendering updates must keep those windows attached too.
+    const replacementMark = this.contentTarget.querySelector(`.anchor-highlight[data-thread-id="${threadId}"]`) ||
+      this.element.querySelector(`#plan-general-comments [data-thread-id="${threadId}"], #plan-detached-comments [data-thread-id="${threadId}"]`)
     if (replacementMark && this._findOpenPopover() === this._activePopover) {
       this._showThreadPopoverFor(replacementMark)
       return

spec/system/linked_comment_navigation_spec.rb

@@ -0,0 +1,56 @@
+require "rails_helper"
+
+RSpec.describe "Linked comment navigation", type: :system do
+  let(:author) { create(:coplan_user, email: "linked-comment-author@example.com") }
+  let(:plan) { create(:plan, created_by_user: author) }
+
+  %w[light dark].each do |theme|
+    [ "inline", "document", "earlier text", "resolved earlier text" ].each do |kind|
+      it "keeps the linked #{kind} discussion open after rendering in #{theme} mode" do
+        author.update!(theme_preference: theme)
+        version = plan.current_plan_version
+        set_version_fixture(version, content_markdown: "# Review\n\nThe retry budget needs review.")
+        thread = plan.comment_threads.create!(plan_version: version, created_by_user: author,
+          anchor_text: kind == "document" ? nil : "retry budget", anchor_occurrence: 1)
+        thread.comments.create!(author_type: "human", author_id: author.id, body_markdown: "Can we extend the retry window?")
+        thread.update!(out_of_date: true, out_of_date_since_version: version) if kind.include?("earlier text")
+        thread.resolve!(author) if kind.start_with?("resolved")
+
+        visit sign_in_path
+        fill_in "Email address", with: author.email
+        click_button "Sign In"
+        expect(page).to have_current_path(library_page_path(author))
+
+        visit plan_page_path(plan, thread: thread.id)
+        popover = "#comment_thread_#{thread.id}_popover:popover-open"
+        expect(page).to have_css(popover, text: "Can we extend the retry window?")
+
+        # Async renderers announce this after rewriting the document DOM.
+        # The linked discussion must remain readable through every refresh.
+        2.times do
+          page.execute_script(<<~JS)
+            document.querySelector("#plan-content-body").dispatchEvent(
+              new CustomEvent("coplan:highlight-settled", { bubbles: true })
+            )
+          JS
+          expect(page).to have_css(popover, text: "Can we extend the retry window?")
+        end
+
+        if thread.open?
+          within(popover) { find("textarea").fill_in(with: "I can still reply.") }
+          expect(page).to have_field(with: "I can still reply.")
+        end
+        page.save_screenshot(Rails.root.join("tmp/linked-comments/#{kind.tr(' ', '-')}-#{theme}.png"))
+
+        page.driver.browser.action.send_keys(:escape).perform
+        expect(page).to have_no_css(popover)
+        page.execute_script(<<~JS)
+          document.querySelector("#plan-content-body").dispatchEvent(
+            new CustomEvent("coplan:highlight-settled", { bubbles: true })
+          )
+        JS
+        expect(page).to have_no_css(popover)
+      end
+    end
+  end
+end